Abstract [en]

Using a conditioning paradigm, the olfactory sensitivity of CD-1 mice for a homologous series of aliphatic 2-ketones(2-butanone to 2-nonanone) and several of their isomeric forms was investigated. With all 11 odorants, the animalssignificantly discriminated concentrations as low as 0.01 ppm (parts per million) from the solvent, and with two odorants(2-octanone and 5-nonanone), the best-scoring animals even detected concentrations as low as 3 ppt (parts per trillion).Analysis of odor structure–activity relationships showed that the correlation between olfactory detection thresholds of themice for the 2-ketones and carbon chain length can best be described as a U-shaped function with the lowest thresholdvalues at 2-octanone. Similarly, the correlation between olfactory sensitivity and carbon chain length of symmetricalketones (3-pentanone to 6-undecanone) can best be described as a U-shaped function. In contrast, no significantcorrelation was found between olfactory detection thresholds of the mice and position of the functional carbonyl groupattached to a C7 backbone. A comparison between the olfactory detection thresholds obtained here with those obtainedin earlier studies suggests that mice are significantly more sensitive for 2-ketones than for n-carboxylic acids of the samecarbon chain length. Across-species comparisons suggest that mice are significantly more sensitive for aliphatic ketonesthan squirrel monkeys and pigtail macaques, whereas the ranges of human olfactory detection threshold values overlapwith those of the mice with seven of the 11 ketones tested. Further comparisons suggest that odor structure–activityrelationships are both substance class and species specific.